Supplemental financial information - Property, plant and equipment at cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	$ 4,789	$ 4,923
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	127	127
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	$ 2,467	2,753
Buildings and improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost, depreciable lives	5 years
Buildings and improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost, depreciable lives	40 years
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	$ 2,195	$ 2,043
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost, depreciable lives	2 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost, depreciable lives	10 years